1. Field of the Invention
The present invention pertains to a well pump system for producing well fluids. The pump system includes a reciprocating piston downhole pump which utilizes the pressure of a column of hydraulic driving fluid or a gas over liquid accumulator and a column of production fluid for driving the pump. One embodiment uses a mechanical actuating rod and production fluid pressure for driving the pump. The driving fluid may be displaced by a hydraulically driven cylinder and piston type power transfer unit on the surface.
2. Background
In the art of downhole pumps for lifting fluids from wells and other subterranean reservoirs there are several concepts which have been relatively well developed including the so-called sucker rod type pump which comprises a reciprocating piston pump disposed deep in the well at the point from which fluid is to be pumped and which is actuated from the surface solely by an elongated reciprocating rod string. There have also been several developments in downhole well pumps which are hydraulically operated in an effort to overcome some of the disadvantages of the mechanical rod type pump. Typically, prior art hydraulically operated pumps, sometimes known as power oil pumps, comprise a reciprocating piston pump located in the wellbore and having opposed pistons or piston surfaces defining power oil chambers and production fluid chambers, respectively. Hydraulic or "power" oil is pumped down the well through a suitable conduit connected to the reciprocating piston pump for actuating the pump to deliver a charge of production fluid through a delivery line to the surface. In some types of power oil pumps the power oil is mixed with the production fluid in the delivery line as a means of returning the power oil to the surface. Accordingly, this so-called power oil must be suitably treated before it can be recirculated by the power oil delivery pump back to the well pump for further energization of the well pump. This type of hydraulically operated pump is relatively complicated and requires expensive and troublesome filtering systems for treating the fluid which is used as "power" oil. Other types of hydraulically operated pumps have been developed which provide separate delivery and return conduits for the hydraulic "power oil" and, of course, a third conduit is required for the production fluid.
Those skilled in the art will appreciate that the prior art hydraulically operated pumps which utilize either mixed production and power oil or separate closed loop power oil systems can be relatively inefficient. The power oil must be circulated down the hole and returned requiring relatively complex conduit systems, in the case of a separate or isolated power oil circuit, and the circulation of mixed or separate power oil completely down through the supply conduit and through the return conduit results in frictional losses which increase the overall power requirements for a given quantity of production fluid produced. Prior art pumps are also characterized by designs which lift production fluid on both strokes of the pump thereby complicating the pump structure itself.
Known types of well pumping systems also suffer from certain shortcomings such as the inability to be effectively regulated to pump at the desired production rate of the well. In this regard, known types of pumping systems are also at a disadvantage because of the economics of producing from low production or marginal wells, particularly wells for producing petroleum fluids. There must, of course, be economic justification for producing hydrocarbon fluids from subterranean wells. If the pumping costs and the capital equipment costs exceed the expected yield of the well or a low marginal net profit results there is little incentive to develop or produce from such formations and wells.
Accordingly, there has been an ongoing need for a downhole well pump which minimizes the capital equipment cost, may be inserted in a well without substantial modification to the existing well structure, may be inserted in wells which are deviated and cannot be produced using mechanical rod actuated pumps and which should be pumped at very low or variable rates to prevent overpumping the well and damaging the formation characteristics as well as the pump mechanism.
There has also been a need for an improved well pump system which can be conveniently installed in existing wells which are relatively inaccessible or for various reasons cannot be pumped utilizing equipment which extends above the earth's surface at the wellhead or takes up a great deal of room at the wellhead.
Substantially all of the disadvantages of known types of downhole well pump systems have been overcome with the hydraulically operated and combined mechanical and hydraulically operated pump system of the present invention as will be appreciated by those skilled in the art upon reading the following.